The 14C-triolein breath test is a popular alternative to the classical 72- hr fecal fat collection for measuring fat malabsorption because of its simplicity, and the rapidity with which a diagnosis can be made. However, because of the concern for the long term effects of low-level radiation (especially when ingested), this test is generally not used in children or women of child-bearing age. The replacement of the radioactive carbon with its stable isotope (13C) and its detection using an isotope ratio mass spectrometer, has now made the triolein breath test available to any population of subjects. A principal limitation in its use today is the high cost of 13C-labeled triolein. We are proposing a biological approach to the synthesis of triolein which will result in an 18-fold increase in the content of the label. Perlabeled (100% incorporation) 13C-triolein will be produced by the autotrophic growth of a high-oleic oil producing strain of microalgae using 13CO2 as the sole carbon source. It is our hope that the technology developed in this grant will reduce the production costs and enhance the sensitivity of this compound such that a 10-fold reduction in cost per patient test can be realized. By reducing this test cost and eliminating the ingestion of radioactive compounds, the triolein breath test should be more readily available to the clinician for diagnostic uses in women and children.